The invention relates to a diaphragm pump for delivering a fluid, in particular an exhaust-gas aftertreatment medium, such as, for example, an aqueous urea solution. In addition, the invention relates to an exhaust-gas aftertreatment system comprising such a diaphragm pump.
Diaphragm pumps, in particular diaphragm pumps that can be used in exhaust-gas aftertreatment systems, have already been disclosed by the prior art. The German patent application DE 10 2008 043 309 A1 discloses a diaphragm pump having a multi-parted pump housing, the working membrane of which is clamped between two housing parts and can be axially actuated by an electric motor via an eccentric and connecting rod. In order to fix the working diaphragm, the housing parts are axially clamped to one another.
A further diaphragm pump is disclosed by the published German patent application DE 10 2005 003 583 A1. In this case, the working diaphragm is not actuated via an eccentric connecting rod but rather by a piston, which is operatively connected to an armature of an electromagnet. When current is supplied to the coil assembly of the electromagnet, the armature is pulled in the direction of the coil assembly, wherein the working diaphragm is impinged with a compressive force via the piston connected to the armature. The compressive force causes the membrane to expand into the pump working chamber, i.e. a compression of the medium situated therein, said medium being subsequently discharged via a discharge valve. If current is no longer being supplied to the coil assembly, a spring supported on the armature ensures that armature and piston are restored to their initial positions. The working diaphragm contracts and creates a vacuum in the pump working chamber; thus enabling the intake of fresh medium. In order to impinge the working diaphragm with a compressive force, the piston is guided through the coil assembly. This requires small dimensional and bearing tolerances to be maintained during the manufacture of the piston and/or the armature. In addition, the guide area of the piston and/or the armature is subjected to an increased amount of wear due to friction. On account of the length of the piston, said piston can furthermore tilt, whereby the frictional forces and consequently the wear increase.
The German patent application DE 10 2004 011 123 A1 discloses a further diaphragm pump having a lifting solenoid as a drive, in which diaphragm pump the working diaphragm is directly connected to an armature of the solenoid that is embodied as a hollow cylinder. A piston for actuating the working membrane can thus be eliminated. The armature is accommodated in a sleeve-shaped sliding bearing. The lifting motion of the armature is delimited by the housing of the electromagnet, which can lead to an undesirable noise generation when the armature strikes the housing.
The German patent application DE 10 2008 054 686 A1 discloses a diaphragm pump comprising an electromagnet for actuating the working diaphragm, in which pump an elastic element embodies both a flat armature that interacts with the electromagnet and a return spring. In order to connect to the working membrane, the elastic element is encapsulated by the plastic of the working diaphragm. A radial guidance of the armature is therefore not necessary, whereby the wear in the region of the moving components is reduced. Due to the design of the flat armature, a compact arrangement is moreover created which only requires a small installation space.